Effects of variable, ice-ocean surface properties and air mass transformation on the Arctic radiative energy budget

Abstract

Abstract. Low-level airborne observations of the Arctic surface radiative energy budget are discussed. We focus on the terrestrial part of the budget, quantified by the thermal-infrared net irradiance (TNI). The data have been collected in cloudy and cloud-free conditions over and in the vicinity of the marginal sea ice zone (MIZ) close to Svalbard during two aircraft campaigns in spring of 2019 and in early summer of 2017. The measurements, complemented by ground-based observations available from the literature and radiative transfer simulations, are used to evaluate the influence of surface type (sea ice, open ocean, MIZ), seasonal characteristics, and synoptically driven meridional air mass transports into and out of the Arctic on the near-surface TNI. The analysis reveals a typical four-mode structure of the frequency distribution of the TNI as a function of surface albedo, sea ice fraction, and surface brightness temperature. Two modes prevail over sea ice and another two over open ocean, each representing cloud-free and cloudy radiative states. Characteristic shifts and modifications of the TNI modes during the transition from winter towards early spring and summer conditions are discussed. Furthermore, the influence of warm air intrusions (WAIs) and marine cold air outbreaks (MCAOs) on the near-surface downward thermal-infrared irradiances and the TNI is highlighted for several case studies. It is concluded that during WAIs the surface warming depends on cloud properties and evolution. Lifted clouds embedded in warmer air masses over a colder sea ice surface, decoupled from the ground by a surface-based temperature inversion, have the potential to warm the surface more strongly than near-surface fog or thin low-level boundary layer clouds, because of a higher cloud base temperature. For MCAOs it is found that the thermodynamic profile of the southward moving air mass adapts only slowly to the warmer ocean surface.

MOSAiC-ACA and AFLUX - Arctic airborne campaigns characterizing the exit area of MOSAiC

“…Turbulent fluxes are not provided in the dataset. This is left for the data user and can follow the examples given in 18,31,32 . We stress that only such flight sections should be considered for the derivation of turbulent fluxes where the aircraft is flying in a straight line.…”

Airborne observations of the surface cloud radiative effect during different seasons over sea ice and open ocean in the Fram Strait

“…In consequence, a realistic representation of the impact of clouds within the Arctic climate system in numerical weather and climate models appears crucial. In particular, the radiative energy budget (REB) of the surface and the atmosphere is largely determined by the presence and properties of clouds (Wendisch et al, 2022b). The REB is quantified by the difference of downward and upward irradiances, F ↓ and F ↑ , respectively; it is referred to as net irradiance F net , with:…”

“…In summer, no significant differences were found. Since the temporal dependence of the thermodynamic adjustments to cloud dissipation complicates an accurate and continuous quantification of this effect (Walsh and Chapman, 1998;Wendisch et al, 2022b), differences between both approaches will remain and likely depend on cloud type, season, and surface conditions. In contrast, the conceptual differences resulting from the cloud-induced surface albedo change can be reduced for the radiative-transfer approach.…”

Evaluation of methods to determine the surface mixing layer height of the atmospheric boundary layer in the central Arctic during polar night and transition to polar day in cloudless and cloudy conditions

“…Furthermore, the ABL does not develop a residual layer due to the absence of a diurnal cycle for most of the year, and even during the polar day, convection typically plays a minor role (Persson et al, 2002;Tjernström and Graversen, 2009;Morrison et al, 2012;Brooks et al, 2017). Within this study, we refer to two typical states of the Arctic ABL observed over sea ice in winter and early spring: a cloudless ABL with a surface-based temperature inversion and a cloudy ABL with pronounced cloud-top inversion (Tjernström and Graversen, 2009;Stramler et al, 2011;Morrison et al, 2012;Wendisch et al, 2023b). We have distinguished between those two states of the atmosphere, as many models have difficulties reproducing the bimodal distribution of the terrestrial radiation (Solomon et al, 2023).…”